2003 Altima with the ABS light coming on occasionally. Checked the pads and rotors and all is moving freely with even wear on both sides. Have now drained the brake fluid and replaced with Dot 3. Bench bled the master and subsequently bled each caliper from rear to front. Pedal pumps hard and holds. When the engine is started, the brake pressure drops and there are no brakes - only slight stopping when the pedal is pumped. Would this mean there is air in the ABS unit, and if so, can it be bled? Are there other possibilities?

so all std brakes are good? pads, rotors and calipers? if not and are bad ABS goes mad, ABS is last to fix, not first OK>
abs can not hid for example, a brake caliper piston rusted to *****
after 19 years..old.(and will be that old I say how can it no be so?>)
all that and not one DTC posted (ALL) HERE ? amazing this...

and when you replace any part here, reset the all DTC now with the scan tool, buy one, you can not fix (diy) modern cars with no tool.
or rotor guide pins seized, fix the mechanical brakes first.!!!
they all must be good, end to end ,sure a weak pad (a tad) the ABS can hide it. well kinda. (normal wear yes, ugly no)
or take the car to a real brake shop and watch them and learn the craft and skills. or take An ASE brake course.
nobody here can guess what is wrong or done wrong, that be impossible other than a simple pep talk,.

Were both sides worn down equally ?
Are the rear brakes adjusted up correctly ?
Is the ABS warning light on ?

This symbol is for worn brake pads. When the pads wear down the sensors make electrical contact with the disc rotor and the light comes on as the circuit is completed. Check out brake pads all round, inmost cases the pads at the front wear down first. Check symmetry of wear. The pads should wear symmetrically and evenly either side of the brake disc. If the pads are wearing on just one side of the disc check that the caliper body is not seized and that the brake guide pins are allowing freedom of movement. It is always a good idea to replace all the pads on one axle at the same time as this ensures even braking. Remember, after replacing pads to pump the brake pedal until stiff prior to moving off so that you can be sure that you can stop when you have to.

This is most likely a problem in your ABS control module. Have it checked, after you check the brake pads for wear. The TCS warning will sometimes come on when the ABS brakes fail to function correctly or the pads are worn too far. This is caused by a brake not releasing as it should or if the caliper is extending too far to properly stop the vehicle. I would not delay in having this checked out as it could lead to brake failure.

The ABS reluctor ring is mounted on the back of the rotor by three fasteners. They do NOT come with the new rotor. IF you did not transfer that part, there would be nothing for the sensor to get it's signal or (sine wve) from. That would set codes. Did you transfer abs ring along with the hub when putting on the new rotors ?

probably a dumb question, but if there is a backing plate, did you make sure it isnt bent and hitting the rotor? you never want to sand new rotors, although i dont think it would cause this concern. i would suggest lightly scuffing up the brake pads. this will eliminate any noise caused by the contact of the rotors and pads. if it goes away then you know its a problem with the pads/rotors.

scoring of only the inside rotors would make me think that possibly the caliper slides are frozen up. make sure they move quite freely on the slides. it is not uncommon for brake pads to score rotors though.

but brake noises at low speeds that dont' change when applying light brake pressure are usually some sort of metal or something contacting the rotor.

The grinding sound when braking is almost surely worn brake pads. If an abs sensor is bad it will set the abs light on. Heres an easy way to figure whether to look at the front or rear brakes first. When braking, take notice as to whether the vibration is felt more in the steering wheel or the seat. If it is more in the steering wheel take a look at your front brakes first, and obviously if it is felt in the seat look at the back brakes first. Both front and rear need to be checked out because the pulsating you are feeling is due to rotors or drums that have been heated up and warped. In order to fix both problems, you most likely will need brake pads and rotors/drums. If you just replace the pads, not only will the pads wear away faster due to the damage to the rotors/drums, but your vibration issue will not go away and infact may intensify.

Sounds like the caliper on the side that isn't wearing is not working properly. You need to test it to make sure that it is pushing out properly when the brakes are pressed. I can't imagine that it is working correctly. It sounds like the piston isn't moving out and you need to look at replacing that caliper so that your brakes wear evenly and also to make sure you have your full stopping power. Good luck and thanks for using FixYa!

make sure that the abs connect for that side is connect properly and the right amount of brake fluid is there

there is a fault code in the ABS system need a code to help you further